The present invention relates to a liquid crystal display apparatus and a liquid crystal projection display apparatus, which employ a hologram color filter. More particularly, the present invention relates to a liquid crystal display apparatus and liquid crystal projection display apparatus, which are designed so that the illuminating light utilization efficiency is improved to a considerable extent, and that a color image can be faithfully displayed with excellent color reproducibility without uneven color or other similar problem.
In conventional color liquid crystal display apparatuses that employ an absorption color filter formed by using pigments, dyes, etc., back light for display is indispensably needed. However, when white light is merely applied to a color liquid crystal display apparatus from the rear thereof, the light utilization efficiency is exceedingly low. Main reasons therefor are as follows:
{circle around (1)} The black matrix, which is a region of the color filter other than cells of each color, occupies a relatively wide area, and light that strikes on the black matrix is wasted.
{circle around (2)} In white light that is incident on each pixel, color components passing through color filter cells of R (red), G (green) and B (blue) are limited; therefore, other complementary color components are wasted.
{circle around (3)} There is a loss of light due to absorption in the color filter.
FIG. 15 shows a conventionally known method designed to solve these problems. A microlens array 2, for example, is installed in front of a color filter 1, and white back light 3 is converged on each of color filter cells R, G and B, thereby raising the utilization efficiency of the back light 3. It should be noted that, in FIG. 15, reference numeral 4 denotes a black matrix which is provided to lie between the color filter cells R, G and B.
However, even if this method is adopted, the white light 3 cannot dispersedly be applied to each of the color filter cells R, G and B. Therefore, the above-described problem {circle around (2)} still remains unsolved.
Japanese Patent Unexamined Publication (KOKAI) No. 4-60538 proposes a liquid crystal projector in which the light utilization efficiency is improved by using three dichroic mirrors and a microlens array without employing a color filter such as that described above. In this case, there is no need for an absorption color filter, which is formed by using pigments, dyes, etc., as in the above-described arrangement. Accordingly, the above problems {circle around (1)} to {circle around (3)} are solved, and thus the brightness of the color image increases. However, since three dichroic mirrors are required, the optical system and the display apparatus increase in size and become bulky. Further, the cost also increases.
In view of these circumstances, the present applicant has proposed a liquid crystal display apparatus in which a color filter that makes use of hologram is employed in order to markedly improve the utilization efficiency of illuminating light, for example, back light for liquid crystal display (for example, see Japanese Patent Application No. 5-12170).
Further, the present applicant has proposed a liquid crystal projection display apparatus in which the above-described liquid crystal display apparatus that employs a hologram color filter is transformed into a projection type display apparatus to display a bright color image on a screen (for example, see Japanese Patent Application NO. 5-242292).
However, it has been found that, when a liquid crystal display apparatus that employs a hologram color filter as described above is used as a projection apparatus, a part of light that is diffracted by the hologram color filter may enter not a liquid crystal cell for displaying the corresponding color but a liquid crystal cell for displaying another color, which is adjacent to the desired cell, and there is therefore likelihood that a color image displayed on the liquid crystal display apparatus will not be projected with faithful color reproduction.
It has also been found that, since light rays that are diffractively dispersed by the hologram color filter enter the liquid crystal display apparatus at different angles according to their wavelength and emanate therefrom at different angles, if these light rays are projected simply by using a projection lens, different colors are undesirably put on the left and right peripheral portions of the screen.
Further, studies should be carried out on the following matters: conditions for the parallelism of back light which are demanded for such a liquid crystal projection display apparatus employing a hologram color filter to display a color image with excellent color reproduction; the positional relationship between the hologram color filter and the polarizer of the liquid crystal display apparatus which is required to reproduce an image clearly and faithfully; and the structure of a hologram comprising uniform interference fringes whereby a higher back light utilization efficiency is provided.
In view of the above-described circumstances, an object of the present invention is to provide a liquid crystal display apparatus and liquid crystal projection display apparatus which employ a hologram color filter, and which are designed so that the illuminating light utilization efficiency is improved to a considerable extent, and that a color image can be faithfully displayed with excellent color reproducibility without uneven color or other similar problem.
To attain the above-described object, the present invention provides a liquid crystal display apparatus in which a hologram which diffractively disperses incident light so as to emanate light rays in different wavelength regions at a predetermined spatial period is used as a color filter for a color liquid crystal display device, and a cut-off filter whose transmittance for light in a desired wavelength region is not higher than 5% is disposed in an optical path which extends from a light source to an observation position.
In addition, the present invention provides a first liquid crystal projection display apparatus which employs a hologram color filter, and in which an image displayed on a color liquid crystal display device is projected on a screen as an enlarged image by a projection optical system. In the projection display apparatus, a hologram which diffractively disperses incident light so as to emanate light rays in different wavelength regions at a predetermined spatial period is used as a color filter for the color liquid crystal display device, and a cut-off filter whose transmittance for light in a desired wavelength region is not higher than 5% is disposed in an optical path which extends from a light source to the screen.
In this case, it is preferable to dispose any of the following cut-off filters in the optical path extending from the light source to the screen: a short-wavelength cut-off filter whose transmittance for a wavelength not longer than 430 nm is not higher than 5%; a long-wavelength cut-off filter whose transmittance for a wavelength not shorter than 660 nm is not higher than 5%; a band cut-off filter whose transmittance for a wavelength in the range of from 490 nm to 510 nm is not higher than 5%; and a band cut-off filter whose transmittance for a wavelength in the range of from 570 nm to 590 nm is not higher than 5%.
It should be noted that a hologram type reflection filter may be used as either of the above band cut-off filters.
It is preferable to dispose the hologram at a position which is closer to the light source than a polarizer which is provided at the entrance side of the color liquid crystal display device.
Further, illuminating light for the hologram preferably has such a degree of parallelism that a component of the light which is at an angle within xc2x16xc2x0 with respect to the travel direction of the illuminating light accounts for not less than 80%.
The dispersion angle of the hologram is preferably within xc2x115xc2x0.
It is preferable for the hologram to have both a dispersing function and a converging function or only a dispersing function. In the latter case, the color liquid crystal display device is preferably provided with a converging optical element in combination with the hologram. In the latter case, a hologram comprising a blazed holographic diffraction grating may be used as a hologram having a dispersing function.
In addition, the present invention provides a second liquid crystal projection display apparatus which employs a hologram color filter, and in which an image displayed on a color liquid crystal display device is projected on a screen as an enlarged image by a projection optical system. In the projection display apparatus, a hologram which diffractively disperses incident light so as to emanate light rays in different wavelength regions at a predetermined spatial period is used as a color filter for the color liquid crystal display device, and a field lens is disposed in the vicinity of the exit side of the color liquid crystal display device.
In this case, the dispersion angle of the hologram is preferably within xc2x115xc2x0.
It is preferable for the hologram to have both a dispersing function and a converging function or only a dispersing function. In the latter case, the color liquid crystal display device is preferably provided with a converging optical element in combination with the hologram. In the latter case, a hologram comprising a blazed holographic diffraction grating may be used as a hologram having a dispersing function.
The field lens is preferably a Fresnel lens.
Further, it is preferable to dispose a cut-off filter whose transmittance for light in a desired wavelength region is not higher than 5% in an optical path which extends from a light source to the screen. More specifically, it is preferable to dispose any of the following cut-off filters: a short-wavelength cut-off filter whose transmittance for a wavelength not longer than 430 nm is not higher than 5%; a long-wavelength cut-off filter whose transmittance for a wavelength not shorter than 660 nm is not higher than 5%; a band cut-off filter whose transmittance for a wavelength in the range of from 490 nm to 510 nm is not higher than 5%; and a band cut-off filter whose transmittance for a wavelength in the range of from 570 nm to 590 nm is not higher than 5%. It should be noted that a hologram type reflection filter may be used as either of the above band cut-off filters.
It is preferable to dispose the hologram at a position which is closer to the light source than a polarizer which is provided at the entrance side of the color liquid crystal display device.
Further, illuminating light for the hologram preferably has such a degree of parallelism that a component of the light which is at an angle within xc2x16xc2x0 with respect to the travel direction of the illuminating light accounts for not less than 80%.
In addition, the present invention provides a liquid crystal display apparatus employing a hologram color filter. The liquid crystal display apparatus has a liquid crystal panel in which liquid crystal cells for displaying pixel information of different colors are periodically arranged, and in which the transmission condition of each liquid crystal cell is controlled independently of each other. The liquid crystal display apparatus further has a color filter which is integrally bonded to the illuminating light entrance side of the liquid crystal panel. The color filter comprises a single hologram which diffractively disperses incident illuminating light so that light rays in different wavelength regions enter respective liquid crystal cells of corresponding colors.
In this case, it is preferable for the hologram color filter to be integrally bonded to the illuminating light entrance side of a transparent substrate.
In addition, the present invention provides a liquid crystal display apparatus employing a hologram color filter. The liquid crystal display apparatus has a liquid crystal panel in which liquid crystal cells for displaying pixel information of different colors are periodically arranged, and in which the transmission condition of each liquid crystal cell is controlled independently of each other. The liquid crystal display apparatus further has a color filter which is integrally bonded to the illuminating light entrance side of the liquid crystal panel. The color filter comprises a stack of holograms or a multi-recorded hologram which diffractively disperses incident illuminating light so that light rays in different wavelength regions enter respective liquid crystal cells of corresponding colors.
In these liquid crystal display apparatuses, it is preferable that an anti-reflection layer for preventing surface reflection should be provided on the illuminating light entrance side of the hologram color filter. It is also possible to provide a prism for preventing surface reflection on the illuminating light entrance side of the hologram color filter.
Further, a polarizer for converting illuminating light into linearly polarized light may be provided on the illuminating light entrance side of the hologram color filter. In this case, however, it is preferable to arrange the polarizer so that the direction of linearly polarized light from the polarizer is normal to the illuminating light entrance surface of the hologram color filter, that is, s-polarized light is incident on the hologram color filter.
It should be noted that these liquid crystal display apparatuses can be used as a liquid crystal display apparatus for a color liquid crystal projector.
In the liquid crystal display apparatus employing a hologram color filter and the first liquid crystal projection display apparatus employing a hologram color filter according to the present invention, a hologram which diffractively disperses incident light so as to emanate light rays in different wavelength regions at a predetermined spatial period is used as a color filter for a color liquid crystal display device, and a cut-off filter whose transmittance for light in a desired wavelength region is not higher than 5% is disposed in an optical path which extends from a light source to an observation position or to the screen. Therefore, the illuminating light utilization efficiency in the projection apparatus can be improved to a considerable extent, and it is possible to prevent crosstalk of colors, e.g. blue and red, and to display or project a color image faithfully with excellent color reproducibility.
In the second liquid crystal projection display apparatus employing a hologram color filter according to the present invention, a hologram which diffractively disperses incident light so as to emanate light rays in different wavelength regions at a predetermined spatial period is used as a color filter for a color liquid crystal display device, and a field lens is disposed in the vicinity of the exit side of the color liquid crystal display device. Therefore, the illuminating light utilization efficiency in the projection apparatus can be improved to a considerable extent, and it is possible to project a color image faithfully with excellent color reproducibility without uneven color or other similar problem.
In another liquid crystal display apparatus employing a hologram color filter according to the present invention, a liquid crystal panel in which liquid crystal cells for displaying pixel information of different colors are periodically arranged, and in which the transmission condition of each liquid crystal cell is controlled independently of each other is prepared. In addition, a color filter is prepared separately from the liquid crystal panel. The color filter comprises a single hologram array or a stack of hologram arrays or a multi-recorded hologram array which diffractively disperses incident illuminating light so that light rays in different wavelength regions enter respective liquid crystal cells of corresponding colors. The hologram color filter is integrally bonded to the illuminating light entrance side of the liquid crystal panel. Accordingly, it is possible to produce a liquid crystal display apparatus employing a hologram color filter without modifying the existing liquid crystal display apparatus manufacturing process to a considerable extent. It should be noted that, since the hologram color filter need not flow through the liquid crystal panel producing process with the hologram layer thereof being incorporated therein, there is no likelihood of the hologram color filter being exposed to high temperature and thus deteriorated.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.